Obese people who eat well and exercise live just as long as their slimmer counterparts and are less likely to die from heart disease, results from a new study suggest.

Researchers used a new rating scale, the Edmonton Obesity Staging System (EOSS), which gauges the progression and severity of the disease.

They found that obese people who scored lower on the scale, meaning they could metabolize fats well and had no other physical or psychological problems, were less likely than the thin group to die from cardiovascular or heart disease.

"Our findings challenge the idea that all obese individuals need to lose weight," lead author Jennifer Kuk said in a statement.

"There are two different groups of obese individuals," Kuk told CTV News on Monday. "Those who do need to lose weight and those who don't."

The study, published Monday in the journal Applied Physiology, Nutrition and Metabolism, looked at 6,000 obese and 23,000 non-obese Americans over a 16-year period.

Researchers attributed the finding partly to "lifestyle behaviours," because obese people who scored lower on the EOSS were more likely to eat healthy, and less likely to diet or smoke.

"These healthy obese people live a healthy lifestyle," Kuk said. "They are more physically fit and they tend to eat more fruits and vegetables."

EOSS identifies four stages of patients:

· Stage 1: patients are obese but have only mild health problems

· Stage 2: patients have moderate cases of high blood pressure and diabetes

· Stage 3: patients have developed life-threatening illnesses

· Stage 4: patients have irreversible kidney or heart damage

Meanwhile a second study published Monday in the Canadian Medical Association Journal found that obese people who had more health problems, and therefore scored higher on the EOSS, faced a greater risk of death.

Researchers in that study based their findings on the responses of 8,143 people to two U.S. National Health and Human Nutrition Examination Surveys.

The EOSS scale relies on traditional measurements of obesity like body mass index, as well as medical conditions associated with obesity such as diabetes or heart disease, to get a picture of their "health-risk profile."

Traditional obesity measures like the body mass index only gauge "how big you area -- not how sick you are," Dr. Arya M. Sharma, who co-authored both research papers, said in a statement.

The study challenges the idea that all overweight patients need to diet, Dr. Yoni Freedhoff told CTV News.

"If they've got no risks, if they've got no problems and they have no desire to try to lose weight, certainly I don't think that we should be thrusting it on them every time they come to their doctors," Freedhoff said.

According to numbers from Statistics Canada, one in four people across the country were clinically obese between 2007 and 2009 -- a rate that has been rising steadily.

With a report from CTV's medical specialist Avis Favaro and producer Elizabeth St. Philip